Recently I have had a number of calls from primary care regarding otitis externa. I have "heard" the reason why, Ha ha!! The product Otosporin has been withdrawn by the manufacturer for unknown reasons and the GPs are now not sure what to use to treat the Pseudomonas aeruginosa they keep growing. Otosporin was a topical combination of hydrocortisone, neomycin (an aminoglycoside) and polymyxin B sulfate. However, the correct question is not what should be used instead of Otosporin, but rather what is the significance of the Pseudomonas aeruginosa and does it need treating at all.

Otitis externa is an acute infection of the skin of the pinna and auditory canal. The common causes are the same as for any skin and soft tissue infections in the body, namely Staphylococcus aureus and Beta-haemolytic Streptococcus Groups A, C and G, not Pseudomonas aeruginosa.If there is discharge from the ear, a pus sample or swab can be sent to the microbiology lab for culture, but it is important to interpret the result with caution. Biomedical Scientists just love growing different bacteria, in fact they excel at it, but this doesn’t mean all these bacteria are clinically significant! A commonly misinterpreted result is the growth of Pseudomonas aeruginosa from ear discharge in otitis externa.Pseudomonas aeruginosa loves to grow in warm moist aerobic environments, so the conditions in the external auditory meatus are perfect for it. These bacteria colonise the ear so when samples are sent to the lab, they grow easily. However, it is almost always not clinically significant BUT there is one very rare exception, called malignant otitis. So how do you know if this is the one rare case?In malignant otitis there is necrosis of the tissue of the ear and the bones of the skull; it is more common in the elderly, diabetics and patients with immunodeficiency. Patients present with severe pain and tenderness associated with discharge from the external auditory meatus and systemic symptoms, such as fever and rigors. Malignant otitis is a potentially life-threatening condition but very rare, there were only 800 cases in the UK between 2012 and 2013. It is an Ear, Nose and Throat (ENT) emergency which should be treated aggressively with systemic antibiotics such as IV Piptazobactam or Ciprofloxacin for 4-6 weeks; as it is a type of osteomyelitis after all.Young fit people don’t seem to get malignant otitis but they do still need their common otitis externa treating correctly. The treatment of otitis externa is to clean out and dry the ear, removing any infected debris; this may need doing more than once. This should be enough to cure most patients without the need to give antibiotics.However, if the problem persists, an antibiotic could be considered. The antibiotic should be active against the common causes, Staphylococcus aureus and the Beta-haemolytic streptococci. Appropriate choices include oral Flucloxacillin, Erythromycin or Doxycycline for 7-10 days.All too often topical agents combining antibiotics with steroids are used (such as Otosporin) but in my experience they are of limited value; after all we wouldn’t consider treating cellulitis of another part of the body with topical antibiotics, the dosing is just too variable, so why would we think it would work in the ear? If the steroid in the topical agent doesn’t damp down the inflammation, samples sent from the ear tend to grow Pseudomonas aeruginosa resistant to the topical antibiotic. The ointment keeps the ear warm and wet and the variable concentration of antibiotic helps select out resistant bacteria.So in answer to the recent surge in questions about what topical antibiotic to use to treat Pseudomonas aeruginosa in otitis externa, the answer is none. Good cleaning and drying of the ear is almost always enough, and if the patient doesn’t get better consider treating the normal causes of otitis externa such as Staphylococcus aureus or Beta-haemolytic Streptococcus Groups A, C or G with oral antibiotics. Maybe it’s actually a good thing that Otosporin has been withdrawn.